This invention relates to a hydraulic control apparatus for tractors, and more particularly to an apparatus in which a position control valve provided for controlling a first hydraulic unit for lifting and lowering primary working implements is operable also for controlling a second hydraulic unit for lifting and lowering secondary working implements and which includes a control lever invariably and automatically returnable to its neutral position upon being released from the hand when the valve is used for controlling the second hydraulic unit.
Generally tractors incorporate a first hydraulic unit equipped with a position control valve for operating a rotary tiller unit, trencher or like primary working implement to be mounted on the rear portion of the tractor, such that the working implement is retainable at the desired level by the operation of the control valve. In addition, tractors are adapted for use with a secondary working implement such as a soil removing plate, front loader or the like to be attached to the front of the tractor which implement is operated by a second hydraulic unit. However, since the control valve is operable only for the first hydraulic unit for the primary working implement, the second hydraulic unit for the secondary working implement is usually controlled by an auxiliary control valve provided for the above-mentioned control valve or by another control valve independently provided. The additional control valve makes the overall construction complex, large and costly therefore.
To render the position control valve for the first unit usable also for the second hydraulic unit, a range for hydraulically operating the secondary working implement must be set on the guide plate for the control valve, but since the control valve is intended for position control, difficulties are encountered in determining the neutral position of the lever as well as in ensuring smooth operation of the primary working implement.